1. Field of the Invention
The present invention relates to a throwaway tip and a throwaway-type cutting tool, such as an end-mill, to which the throwaway tip is mounted.
2. Description of the Related Art
Hitherto, in some throwaway-type end mills in which a plurality of, for example, two, parallelogram plate-like throwaway tips are mounted to the distal end of a tool body, and which are capable of performing a boring operation, one tip has been arranged so that a long cutting edge is defined as a front cutting edge and a short cutting edge is defined as an outer peripheral cutting edge, and the other tip has been arranged so that a short cutting edge and a long cutting edge is defined as a front cutting edge and a long cutting edge is defined as an outer peripheral cutting edge.
In this case, if the two tips have the same shape and size, they are conveniently administered or replaced. When such an end mill is used for a shoulder-cutting operation or a drilling operation with the outer peripheral cutting edges provided along the rotation axis of the tool body, for example, when the front cutting edge of one tip is provided so that an outer-peripheral corner-side cutting edge is projected at the distal end to gradually incline inward to a base end, the inner corner cutting edge of the outer tip will project toward the distal end from the outer-peripheral-corner-side cutting edge, so that the front cutting edge is easily chipped at low speed.
In order to overcome such a drawback, when the front cutting edge of the other tip is arranged in a radial direction so as to prevent the inner corner cutting edge from projecting toward the distal end, since the outer peripheral cutting edge of the other tip is inclined inward from the outer peripheral cutting edge of one tip and does not serve as the outer peripheral cutting edge, the outer peripheral cutting edge performs cutting with a single edge of one tip so that the front cutting edge is easily chipped and cutting efficiency is low.
As an invention for improving such a defect, Japanese Unexamined Patent Application Publication No. 10-291115 discloses an end mill. In the end mill two types of parallelogram plate-like tips are used, which are in line symmetry and are rotated in opposite directions. A short cutting edge of one tip is used as a front cutting edge, and a long cutting edge of the other tip is used as a front cutting edge thereby adopting an arrangement such that an outer peripheral corner-side cutting edge of each of the front cutting edges is projected toward the distal end from an inner corner cutting edge. This can perform a cutting operation using outer peripheral corner-side cutting edges as two cutting edges, and can improve cutting efficiency by restricting chipping of the outer-peripheral-corner-side cutting edges.
In such a end mill, however, two types of tips having different outer shapes should be prepared, thereby making administration and replacement complicated, running costs increase, and the cost of manufacturing the tip increase.